PA33.4 | Common Skin Tumors & Morphology — Summary & Reflection

REFLECT

Before you move on, pause and answer these in your head:

1. If a practical slide shows basaloid cells and you have to distinguish SK from BCC in 30 seconds — what single histological feature makes the call? (Horn cysts → SK; peripheral palisading + retraction cleft → BCC)

1. A patient has a 7 mm lesion with four shades of color and an irregular border — you send a shave biopsy. The report says 'full-thickness epidermal atypia with intact basement membrane.' Is this melanoma, or something else? (Intact BM = Bowen disease/SCC in situ, NOT invasive melanoma — but clinical features should still prompt re-excision and re-assessment)

1. Which single measurement determines stage and prognosis in melanoma, and how is it measured? (Breslow thickness in mm, from top of granular layer to deepest invasive cell)

If you paused on any of these, mark that section for re-read before your practical.

KEY TAKEAWAYS

Key takeaways from this SDL:

• Seborrheic keratosis = stuck-on + basaloid + horn cysts. Entirely benign. The most common benign epidermal tumor.

• Adnexal tumors recognition trio: tadpole ducts (syringoma), jigsaw basaloid nests with hyaline sheath (cylindroma), ghost cells + calcification (pilomatricoma).

• Melanocytic nevi mature from junctional → compound → intradermal; maturation (cells becoming smaller deeper) = benign. Loss of maturation = alarm signal.

• AK vs Bowen: AK = partial-thickness (basal) dysplasia; Bowen = full-thickness dysplasia, intact BM. Both are premalignant.

• BCC: most common skin cancer, local destruction without mets; peripheral palisading + retraction cleft is the diagnostic key.

• SCC: second most common; keratin pearls + intercellular bridges + dermal invasion; real metastatic risk; Marjolin's ulcer is aggressive.

• Melanoma: most dangerous; ABCDE clinically; pagetoid spread + vertical growth phase + Breslow thickness histologically.

• Dermatofibroma: storiform spindle cells + dimple sign + epidermal hyperplasia; entirely benign.

• Cutaneous metastases: primary histotype in dermis, epidermis spared; Sister Mary Joseph nodule = umbilical met from GI/pelvic cancer.

For the practical exam: always describe clinical pattern, site, gross appearance, then move to histological pattern systematically. Use the Master Recognition Table as your final preparation tool.